The mechanistic target of rapamycin (mTOR) controls cell growth by integrating a wide range of signals, such as growth factors, nutrients, and stress. mTOR is a conserved protein kinase that forms two complexes, referred to as TORC1 and TORC2, with distinct subunit composition and physiological functions. The physiological function of TORC1 in promoting cell growth is well characterized and inhibitors that target the complex are used clinically to treat several diseases including cancer, transplant rejection, and restenosis. The mechanism of TORC1 regulation is a topic of intense interest in both basic cell biology and translational research. Growth factors and nutrients activate TORC1 to promote cell growth by stimulating anabolism and inhibiting catabolism. Previous studies have investigated TORC1 regulation by growth factors and nutrients. However, the molecular insights of inhibitory signals that regulate TORC1 are ambiguous. Both oxidative stress and hyperosmotic stress rapidly and potently inhibit TORC1. Our preliminary studies indicate that the nemo like kinase (NLK) plays a crucial role in TORC1 inhibition in response to hyperosmotic or oxidative stress. In addition to oxidative and hyperosmotic stress, we observed that protein kinase A (PKA) mediates an inhibitory effect to mTORC1 in response to the second messenger cyclic AMP (cAMP). The long-term goal of this project is to elucidate the molecular mechanisms of TORC1 regulation and the function of TORC1 in cell physiology and disease. In this proposal, we will determine the biological function and molecular mechanism of NLK in mediating the osmotic and oxidative stress to inhibit TORC1. Furthermore, we will investigate the mechanisms of mTORC1 inhibition by PKA and functional cross talk between cAMP and mTORC1. The specific aims for this proposal are: 1. Determine the function of NLK in TORC1 regulation by osmotic and oxidative stress 2. Elucidate the biochemical basis of NLK in TORC1 inhibition by osmotic and oxidative stress 3. Investigate the molecular mechanisms and functional role of TORC1 inhibition by cAMP-PKA